1. Field of the Invention
The present invention relates to a force/tactile display for receiving force/tactile presentation from a virtual environment, a method for controlling the force/tactile display, and a computer program, particularly to a force/tactile display that presents grasp sensation to a plurality of fingertips, a method for controlling the force/tactile display, and a computer program.
More specifically, the invention relates to a grasp-type force/tactile display that presents each of a plurality of fingertips with the action point indicating which portion of the fingertip is in contact, a method for controlling the force/tactile display, and a computer program, particularly to a force/tactile display that smoothly presents the action point in response to discontinuous collision events between a fingertip and an object, a method for controlling the force/tactile display, and a computer program.
2. Description of the Related Art
In the technical fields of virtual reality and tele-reality, a force/tactile display or a “haptic device” may be essential to present an operator with not only visual and auditory information but also force and tactile sensation.
Recent improvements in computing speed and advances in simulation technology have allowed real-time simulation of a virtual environment in which a plurality of objects are present at the same time and physical interaction, such as collision and contact, occurs among the objects. An ability to calculate collision between objects and the contact force generated there between in an accurate, real-time manner taking dynamics into consideration allows a user to be presented with realistic sensation when the user touches or grasps an object in the virtual environment through a haptic device by using a motor to actually produce the calculated force.
Haptic devices have found a wide variety of applications. Three-dimensional force sensation and tactile sensation of an object in an actually inaccessible environment can be presented, for example, in mastering medical and other special skills, and in remote manipulation in a virtual environment, such as a microcosm and the ocean, and in a special or hazardous environment, such as an atomic reactor. As the scale and accuracy of a virtual space that can be processed in a real-time manner increase, the demand for a force/tactile display is expected to increase in the future.
A typical example of the haptic device is of stylus type using a serial link shown in FIG. 10. A user grasps the front-end portion of the stylus, where moments of force around three to six axes are presented (see http://www.sensable.com/haptic-phantom-desktop.htm (as of Feb. 3, 2007), for example).
As a structure that solves insufficient rigidity of a serial link, there has also been proposed a haptic device using a parallel link structure to present moments of force around three to six axes as shown in FIG. 11 (see Japanese Patent No. 3329443, http://forcedimension.com/fd/avs/home/products/ (as of Feb. 3, 2007), and http://www.quanser.com/industrial/.html/products/fs—5dof.as p (as of Feb. 3, 2007), for example).
Any of the haptic devices using these link mechanisms presents force/tactile sensation at only one point in the grasp position. In other words, such a haptic device is not designed to present force/tactile sensation to each of the fingers of the operator independent of each other. Therefore, such a device cannot present the sensation when the fingers grasp a virtual object.
On the other hand, a multi-fingered haptic device has a function of using a master hand that remotely operates a slave hand, such as a robot hand, to convey the motion of the master hand (operation means) to the slave hand (manipulation means) and presenting force sensation of the slave hand to the master hand. That is, the operator on the master side can feel as if he/she were directly acting on the object being manipulated.
To present force to multiple fingers, there has been proposed a haptic device in which a finger is connected to remote motors with wires through which forces are applied as shown in FIG. 12 (see http://sklab-www.pi.titech.ac.jp/frame_index-j.html (as of Feb. 3, 2007), for example). In such a device configuration, however, it is necessary to typically control the wires in such a way that they will not be loose, so that the control tends to be complicated. Further, the wires likely interfere with one another, so that the range of motion, particularly rotation, is not very large.
There has also been proposed a haptic device in which a hand-type force presentation mechanism is added to a manipulator opposed to a human hand as shown in FIG. 13 (see Haruhisa Kawasaki, Takumi Hori, and Tetsuya Mouri, “Multi-fingered haptic interface opposed to a human hand” (the Robotics Society of Japan, Vol. 23, No. 4, pp. 449-456, 2005), for example). There has been proposed a method similar to this method, in which a hand-type force presentation mechanism is added to the tip of an exoskeleton (see http://www.immersion.com/3d/products/cyber_grasp.php (as of Feb. 4, 2007), for example). There has also been proposed a system in which a finger stall is attached to the tip of the serial link described above and three-axis forces are presented to the finger (see Japanese Patent No. 3624374, for example).
Any of the haptic devices of the related art described above can present only a translational force to a fingertip, but cannot present which portion of the fingertip is in contact, that is, the action point. It can therefore hardly be said that such a haptic device presents grasp sensation to a plurality of fingertips in a satisfactory manner.
To present the contact position on a fingertip, it is conceivable to add a degree of freedom for force control for moment presentation to the force presentation device attached to the finger. Such a method, however, may typically require a motor having a relatively large output, so that the resultant mechanical structure is inappropriate for force presentation to multiple fingers because the weight of the entire structure increases and the force presentation devices attached to the fingers likely interfere with one another.
Further, position control of the action point causes a problem of delay of action point presentation in response to discontinuous collision events between a fingertip and an object.